havesomeseichel-
The dimes. Although circles of a different diameter will fill an equal area in a square, the thickness of the dimes is less than the nickels.
Additional hint coming up forthwith.
Feivel-
Thank you.
Weigh 1 from stack 1, 2 from 2 and three from 3 together, then see if you are short 1,2 or 3.